FIELD OF THE INVENTION
The present invention relates to a device for detecting the intrusion of a body into a predetermined space and, more particularly, to a device of this type comprising a transmitter transmitting ultrasound into said space, a sensor which senses the echoes from the transmission by the transmitter into said space in order to deliver a signal representative of said echoes, and electronic means for processing said signal in order to diagnose the possible presence of a moving body in said space.
Such devices are known, designed in particular to trigger an alarm following detection of unauthorized intrusion into a space such as the interior of an automobile vehicle, for example. This is a situation encountered, in particular, when a thief enters by breaking into this interior.
In known detection devices, the ultrasound transmitter and the echo sensor are both mounted in fixed positions, inside the interior. In order to cover the entire volume of this interior optimally, it is then necessary to fix this transmitter and this sensor in positions of compromise between various positions which each provide optimum coverage of only a part of this volume. The result of this compromise is that certain parts are not monitored optimally. Designers are then forced either to focus the monitoring on particularly sensitive regions (that of the steering wheel, the car radio, the glove box, for example) to the detriment of others, or to increase the number of the transmitter/sensor pairs installed in the interior, which solution has the drawback of being expensive.
Further, document EP 0 293 004 discloses an ultrasonic detection device comprising a transmitter and a receiver which are fixed relative to one another, interacting with a turning reflector placed on the transmitter/receiver axis. Although it allows scanning of the plane perpendicular to this axis, such a device involves a moving reflector which is difficult and expensive to produce and adjust, and only allows those echoes produced on surfaces normal to the axis of the incident beam to be returned to the receiver. This limitation makes it problematic to use in a complexly shaped environment such as an automobile vehicle, in which the echoes occur only rarely in the direction of the reflector, thus making the received signal unusable.